1. Field of the Invention
The present invention relates to a method for manufacturing a heat dissipation structure of a printed circuit board, and more particularly to a method for manufacturing a heat dissipation structure of a printed circuit board for improving the filling capability of plating copper, and improving the uneven surface caused by performing the copper plating process for many times using a nickel plating process.
2. The Prior Arts
FIGS. 1A to 1F are cross-sectional views illustrating the steps of a conventional method for manufacturing a heat dissipation structure of a printed circuit board. Referring to FIG. 1A, a printed circuit board 1 is provided. The printed circuit board 1 includes a first substrate 10, two second substrates 15 respectively disposed on the upper and lower surfaces of the first substrate 10, two inner copper layers 21 each disposed between the first substrate 10 and the second substrate 15, and two outer copper layers 23 each disposed on one outer surface of the second substrates 15. Referring to FIG. 1B, a plurality of openings are formed in the upper layers of the printed circuit board 1 to expose a portion of the inner copper layers 21. The openings include at least one first opening 31 and at least one second opening 33. The first opening 31 is smaller than the second opening 33, and the size of the second opening 33 is larger than or equal to 150×100 μm2. Referring to FIG. 1C, at least one first copper plating layer 25 is formed on the printed circuit board 1. The first opening 31 is fully filled up with the first copper plating layer 25, but the second opening 33 is not fully filled up with the first copper plating layer 25 such that the first copper plating layer 25 filling in the second opening 33 has a first dimple 40 on its top.
Referring to FIG. 1D, a copper plating layer 60 is formed by performing a copper plating process at least once. The copper plating layer 60 is thick so that the dimple 40 can be fully filled up with the copper plating layer 60. A chemical mechanical planarization process is then performed to planarize the surface of the copper plating layer 60.
Referring to FIGS. 1E and 1F, a patterned dry film 50 is formed on the surface of the copper plating layer 60. After an etching process and a removal of the dry film process, a heat dissipation structure 70 including the first copper bumps 71, the second copper bumps 73, and the copper pads 75 is formed. The heat dissipation structure 70 and the inner copper layers 21 are electrically connected to each other.
In the prior art, because the size of the opening is larger than or equal to the size of 150×100 μm2, the opening is not easily to be fully filled up by performing the copper plating process only once, and thereby the copper plating process must be performed for many times in order to fill up the opening. However, there exists an uneven surface problem caused by the interface between the two adjacent copper plating layers when the copper plating process is performed for many times, which results in the variation of the resistance values. The resistance value will be increased for each copper plating process. Therefore, a polishing process is needed in order to meet the specification of the resistance value, but the polishing process is not easily controlled so that the resistance value cannot be standarized.